1. Field of the Invention
The invention relates to speaker parts, particularly, elastic parts for supporting a part for a vibration system, and a method of manufacturing the speaker parts.
The present application claims priority from Japanese Application No. 2001-121280, the disclosure of which is incorporated herein by reference for all purposes.
2. Description of the Related Art
Conventionally, an elastic part for supporting a vibration system part of a speaker, for example, an edge which is attached on the rim of a diaphragm to support the diaphragm with respect to a frame so as to permit it to vibrate, is manufactured with use of a rubber material, e.g., IIR (isobutylene-isoprene rubber), SBR (styrene-butadiene rubber) type, NBR (acrylonitrile-butadiene rubber), EPDM (ethylene-propylene-ethylenenorbornene rubber). The rubber material used has 50 degrees, 60 degrees, 70 degrees or 80 degrees of hardness in the main.
However, the edge formed from such a conventional rubber material has the problem of causing serious difficulties in fine-tuning because variations in the types and/or hardness of the rubber used for the edge effect significant changes in the sound quality of the speaker.
A speaker is typically constructed by installing a diaphragm and a magnetic circuitry unit inside a speaker box. With this mode of construction, in the outputting of sound, when the vibration of the diaphragm pushes the diaphragm toward the front of the speaker box (i.e., outward from the inside of the speaker box), the air pressure inside the speaker box becomes a negative pressure in relation to the outside air.
Thus, in the case of the vibration of the diaphragm toward the front, a force acts on the edge supporting the diaphragm with respect to the frame, so as to retract the edge toward the inside of the speaker box.
Therefore, in a speaker used in an environment at high temperatures, for example, in a vehicle-mounted speaker, when a conventional rubber material for forming the edge is softened by high temperatures, the rubber material loses the strength required to maintain the shape of the edge in the face of the pressure differential between the inside and the outside of the speaker box generated during the vibration of the diaphragm.
Thus, such an edge is unable to respond to the vibration of the diaphragm, which may result in the occurrence of a so-called “suction” phenomenon in which the edge is sucked toward the interior of the speaker box.
That is to say, as shown in FIGS. 8A to 8C, an edge 1 is interposed between a diaphragm 3 and a frame 2 in order to support the diaphragm 3 with respect to the frame 2 so as to allow the diaphragm 3 to vibrate in an inside-outside direction of the speaker box (i.e. in the vertical direction in FIG. 8).
In the condition that the edge 1 maintains its shape of bulging toward the outside of the speaker box (toward the upper side in FIG. 8) as illustrated in FIG. 8, the edge 1 holds the diaphragm 3 in the proper vibration state of between a vibration position toward the interior of the speaker box as shown in FIG. 8B and a vibration position toward the outside of the speaker box as shown in FIG. 8C, with a set position in FIG. 8A between.
However, when the rubber material for forming the edge 1 is softened in the high-temperature environment to decrease the strength of the edge 1, as illustrated in FIG. 9, the edge 1 is retracted toward the interior of the speaker box (toward the lower side in FIG. 9) by the pressure differential between the inside and outside of the speaker box which is generated by the vibration of the diaphragm 3. As a result, the diaphragm 3 is supported by a deformed edge 1 during the vibration between a vibration position toward the interior of the speaker box shown in FIG. 9B and a vibration position toward the outside shown in FIG. 9C, with the set position shown in FIG. 9A between.
This creates the problem of disabling the proper vibration of the diaphragm 3 so as to produce a defective sound or to become a cause of failure.
In particular, in addition to the requirement of reducing the size of speaker boxes due to the downsizing of audio systems, recent years have seen advances in the powering of speakers. This causes an increase in the pressure differential between the inside and outside of the speaker box during the vibration of the diaphragm, leading to a serious problem of the “suction” of the edge as described above.